1. Field of the Invention
This invention relates to power supplies and more particularly to a circuit for the monitoring and control of a power supply furnishing precision regulated voltage to a load.
2. Description of the Prior Art
A free running DC to DC converter is a highly efficient and economical way of converting voltage from one potential level to another potential level. However, a major disadvantage of a free running converter is its poor inherent voltage regulation characteristics. With the continuing growth and complexity of telephone switching systems, the supporting power supply systems have been called upon to furnish a precision regulated voltage with only minor deviations from one potential level to another. Further the power supplies in such systems are required to retain their very high reliability and overload safety characteristics as those in the past while at the same time retaining some degree of efficiency.
The disadvantage of the poor inherent regulation may be readily corrected by inserting a series regulator between the converter output and the load. This solution, however, requires a separate circuit package which dissipates part of the converter's power output and reduces the efficiency.
Another method of regulation is disclosed by a French Pat. No. 1,492,611. A two transistor push-pull oscillator with a transformer and a zener diode voltage reference was used to drive a control transistor, which is in series with a common lead between the feedback winding centertap and the emitters of both oscillator transistors. Regulation is effected by turning the control transistor on to saturation in order to get the highest output voltage on one extreme and by turning the control transistor off to obtain no output voltage on the other extreme. The disadvantage of this circuit occurs during this "other extreme," for it is possible that the leakage current, output capacitance and stray capacitance of the circuit involving the "off" transistor may prevent turning off the "on" transistor.
Another means of effecting regulation was disclosed by U.S. Pat. No. 3,327,199 which issued to Gardner et al on June 20, 1967. Regulation is provided by varying the input voltage to a basic one transformer converter circuit.
Another method providing regulation for a DC to DC converter was disclosed by U.S. Pat. No. 3,427,525 which issued to Thornwall on Feb. 11, 1969. Thornwall achieves regulation by using a switching means to alternately clamp and release a transformer couple regenerative blocking oscillator. The clamping and releasing rates are determined by the relative magnitude of the input and output voltages and by the power required by the load.